Distribution of lysozyme and mucin (MUC2 and MUC3) mRNA in human bronchus.

Immunocytochemical studies have shown that gel-forming glycoproteins (mucins) and the bacteriolytic protein lysozyme are selectively expressed in airway mucous and serous cells, respectively. The mechanisms mediating this selectivity are unknown. In this study, we localized mucin and lysozyme mRNA by in situ hybridization to investigate the possibility that phenotype-specific expression of these proteins is controlled at the level of mRNA. Radiolabelled sense and antisense probes were constructed from the human tracheal mucin cDNA, HAM1 (MUC2 gene), the human small intestinal mucin cDNA, SIB139 (MUC3 gene), and the bovine tracheal lysozyme cDNA, Lys 7a. Frozen sections of human bronchus were hybridized with these probes and washed under routine conditions. Autoradiography showed that although lysozyme mRNA was strictly limited to cells expressing lysozyme, mucin mRNA was present both in mucin-expressing and mucin-non-expressing epithelial cells. This suggests that the restriction of lysozyme to serous cells is controlled at the level of mRNA (synthesis and/or degradation), whereas the restriction of mucin to mucous cells is controlled at the level of translation.